Conventionally, many load driving devices such as motor driving devices or the like and power supply devices incorporate various protection circuits (such as an overcurrent protection circuit, an overvoltage protection circuit, and an overheating protection circuit) to enhance the safety thereof.
Of these protection circuits, a conventional overcurrent protection circuit is in general configured as follows. The conventional overcurrent protection circuit monitors a drive current flowing through an object to be protected (for example, a load or an element provided inside the device). When the drive current has reached a predetermined threshold value and remains in that state for a predetermined time (a noise masking time), the conventional overcurrent protection circuit judges that an overcurrent occurs in the device, and shuts down the operation of the device.
As a conventional technology related to what has been described thus far, an intelligent power switch that provides a comparator with a first threshold value corresponding to a high current that can, if it flows even for a short time, damage a semiconductor switch, that stores in a memory a second threshold value that is smaller than the first threshold value, and, when a detected current value becomes equal to or greater than the first threshold value or the CPU judges that a current greater than the second threshold value is continuously flowing for more than a given period of time, that turns the semiconductor switch off, and a switching device are disclosed and proposed in Patent Document 1.
Patent Document 2 discloses and proposes a switching power supply device that is composed of a fuse, a primary winding of a transformer, a switch element, and a current detection resistor connected in series between a direct-current voltage input terminal and a ground terminal, that makes a control circuit portion perform on/off control of the switch element so as to keep constant an output voltage of a rectifying/smoothing circuit connected to a secondary winding of the transformer, and that performs protection operation when a current detection voltage detected by the current detection resistor exceeds a predetermined threshold value, wherein a protection diode that, when the switch element is short-circuited, makes the fuse blow by passing a high current therethrough by being short circuited upon the application of a voltage exceeding its withstand voltage in the reverse direction is connected in parallel with the current detection resistor so as to be opposite in polarity.
Patent Document 3 discloses and proposes a semiconductor integrated circuit that performs switching control of an operation mode of an H-bridge circuit according to a load current, and a motor driving control system.
Patent Document 1: JP-A-09-331625
Patent Document 2: JP-A-2001-145339
Patent Document 3: JP-B-3665565